1. Field of the Invention
This invention relates to the field of semiconductor heterojunction devices and, in particular to a semiconductor structure which utilizes an inversion channel created by modulation doping to implement thyristors, transistors, optical emitters, optical detectors, optical modulators, optical amplifiers and other opto-electronic devices.
2. State of the Art
This invention builds upon the existing device structure known as the Pseudomorphic Pulsed Doped High Electron Mobility Transistor (Pulsed Doped PHEMT) and sometimes referred to as the Pulsed Doped Modulation Doped Field Effect Transistor (Pulsed Doped MODFET) or the Pulsed Doped Two Dimensional Gas Field Effect Transistor(Pulsed Doped TEGFET). GaAs/InGaAs/AlxGa1-xAs has been the III–V material system of choice for these devices because of the ability to grow high optical/electrical quality epitaxial layers by MBE (molecular beam epitaxy). However, relatively new wideband semiconductors such as GaN are also promising candidates since quantum wells are easily formed. PHEMTs are now in constant demand as the front end amplifier in wireless and MMIC applications and they have become well recognized for their superior low noise and high frequency performance.
The PHEMT has been very successful in producing microwave transistors that operate well into the multi-gigahertz regime, initially being used extensively in military systems and now finding their way into commercial products, particularly in the area of cellular communications. There are a multitude of advantages to be gained by the use of optical signals in conjunction with electrical signals in the high frequency regime. Combining electronic with optoelectronic components monolithically gives rise to the concept of the optoelectronic integrated circuit (OEIC). In general, monolithic integration has proven to be difficult because of the very dissimilar nature of the structures of electronic devices such as the FET on the one hand and the optoelectronic devices on the other hand such as the junction diode laser and the MSM or PIN diode. To make matters even more complicated, the introduction of optoelectronic device combinations must compete with state-of-the-art electronic chip technology which is currently complementary MOS transistors in the form of Si CMOS circuits. The implication is that the introduction of optoelectronic device combinations must provide for complementary device combinations together with optoelectronic functionality. In this way, an optoelectronic technology base would provide both complementary functions and optoelectronic functions which would provide it with a clear cut advantage over conventional CMOS. The PHEMT may be modified for optoelectronics by the use of an ohmic contact to replace the Schottky contact (see U.S. Pat. No. 4,800,415 which is hereby incorporated by reference herein in its entirety). Such a device has been designated an HFET or more precisely an inversion channel HFET (ICHFET) to distinguish it from the broad range of III–V transistors which have been described as HFETs. However, the detailed nature of how the p doping is added to the PHEMT is a critical issue because the resulting structure must perform multiple functions which are 1) it must provide a low resistance ohmic contact, 2) it must provide funneling of carriers into the active region of the optoelectronic device, and 3) it must minimize the effects of free carrier absorption. In order to realize a complementary structure with an ohmic contact modified PHEMT, it is necessary to grow two different types of modulation doped quantum well interfaces, one which creates an inversion channel for electrons and one which creates an inversion channel for holes. The manner in which these two interfaces are combined structurally, affords some unique opportunities for the creation of optical switches in the form of thyristors. These are routinely formed in the implementation of CMOS technology as the series combination of p-n-p-n structures but are intentionally suppressed to eliminate parasitic latch-up. However in the design of the III-V complementary technology layer structure, the thyristor may be optimized to provide unique opportunities for switching lasers and detectors.
It is an object of this invention to devise a single epitaxial layer structure which can simultaneously within a single integrated circuit chip be fabricated to operate as an electron majority carrier bipolar transistor, a hole majority carrier bipolar transistor, a field-effect transistor with electrons as the channel majority carrier, a field-effect transistor with holes as the channel majority carrier, a laterally injected laser in which channel majority carriers are injected from channel contacts and channel minority carriers are injected from an ohmic gate contact, a thyristor switching laser, a thyristor switching detector which absorbs radiation across the bandgap of its quantum well(s), a pin type bandgap detector in which majority photoelectrons are removed to the channel contacts and photoholes are removed to the gate or collector ohmic contact, an optical amplifier and a modulator.
Another object of the invention is to specify a fabrication technology to produce a pair of complementary n-channel and p-channel field effect transistors that function optimally as a complementary logic gate. This fabrication sequence should also produce complementary bipolar field-effect transistors with n-channel and p-channel control elements respectively.
Another object of this invention is to show how the thyristor device may be optimized from the same complementary technology sequence to perform as a high efficiency laser when switched to its on state and as a high efficiency detector in its high impedance off state.
Another object of this invention is to produce an in-plane directional coupler using the complementary structure in which the propagation constants in two parallel waveguides may be altered selectively by the injection of charge into either or both of these guides from self-aligned contacts which may inject charge into the core of their respective waveguides.
Another object of this invention is to show how the optoelectronic devices can be fabricated as vertical cavity devices and yet also provide sources, detectors, modulators, amplifiers and switches that are interconnected by low loss passive waveguides in the plane of the integrated circuit.
It is a further object of this invention to achieve these goals with a unique combination of planar sheet dopings which modify the generic PHEMT structure and provide it with optoelectronic capability.
A final object of this invention is to show how the complementary transistor technology and the optoelectronic device technology are optimized simultaneously for a manufacturable solution.